Although the following description relates to the measurement of visual properties of surfaces, the present invention is suitable for all types of radiation, thus in particular for all kinds of electromagnetic radiation as well as for all measurements of reflection and transmission.
A device for measuring visual properties of surfaces generally has a housing in which an optical unit, respectively a base body (hereinafter referred to as optical measuring base unit) is arranged.
The optical measuring base unit comprises an illuminating means, the light of which is directed at a predetermined angle to the surface to be measured (hereinafter referred to as measurement surface). Further, the optical unit has a detecting means which receives and registers the light reflected from the measurement surface.
Illuminating and detecting means are generally arranged in corresponding receiving means of the optical unit, respectively base body.
When carrying out a measurement, the housing is placed upon a measurement surface and the measurement angles are defined by the alignment of the housing with respect to the surface. Furthermore, the housing construction generally also comprises control and evaluation electronics which receive measurement data and, for example, display same on a display means disposed on the exterior of the housing.
The illuminated area of the measurement surface is that of a predetermined section within the touchdown surface, whereby the touchdown surface and the measurement surface are brought into substantially flush planar contact with one another.
Such devices are used to characterize surfaces including, for example, products with glossy and high-gloss surfaces, goniochromatic surfaces and other such similar surfaces. A surface is goniochromatic if its characteristic optical measurement parameters, for example its color values or its reflection properties, are dependent upon the angle of illumination and measurement during a radiation measurement of said surface.
An important application in this regard is, for example, the analysis of automobile finishes. The finished surfaces are characterized during manufacture or repair in order to evaluate their quality relative to given standards.
Various devices for measuring optical properties, in particular visual properties of surfaces are known from the prior art, as are the corresponding methods thereto. Several of these measuring methods include, for example, measuring luminosity (measurement of intensity), measuring color and polarization, and other associated combined measurements.
Common to known devices and methods is that the measuring means and the measurement surface have to be in precise alignment with one another in order to provide reliable and reproducible measurement results. In other words, the angle of illumination from the illuminating means and the angle of the detecting means relative the measurement surface always have to be the same.
According to the prior art, the alignment of the measuring means to the measurement surface is registered by contact pins which are elastically affixed external the housing.
A typical arrangement is that of three contact pins defining a plane. When the optical measuring base unit is set down parallel to the measurement surface, the three contact pins are pressed inwardly and the corresponding electric contacts are closed. In contrast, when one or more contact pins are not pressed inward or are only pressed inward to an insufficient degree, the measurement is deactivated.
Despite monitoring, faulty measurements can occur.
The task of the present invention is to provide an improved device for measuring reflection and/or transmission properties of objects and surfaces and in particular visual properties of surfaces as well as a method for operating said device.